The objective of the project is preparation of reagents to determine the nature of the transmembrane interactions between proteins. The reagents will be bifunctional and are expected to either (a) crosslink two neighboring transmembrane proteins, (b) attach, by both functional ends, to the portion of a single membrane protein that extends through the membrane. At the present time, all of the reagents being prepared contain spin label groups arranged in the reagent molecule so that EPR spectra will demonstrate whether or not a reagent extends across a membrane.